The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners have also been used for many years in tubeless pneumatic vehicle tires to retard or prevent the escape of air used to inflate the tire, thereby maintaining tire pressure. Rubbers, such as halobutyl and blends of butyl and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of the innerliners.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
The preparation of a gum strip composed entirely of compounded chlorobutyl or bromobutyl rubber or blends of chlorobutyl or bromobutyl rubber with butyl rubber has been observed to have some processing and fabrication problems such as sticking to processing equipment during the milling and calendering operations.
Furthermore, it has sometimes been desired to provide a gum strip composition for the innerliner which has suitable processing properties, sufficient green strength, building tack in its uncured state and cured adhesion to the tire carcass while also having a satisfactory degree of air impermeability.
Halobutyl and butyl rubbers are also the most expensive rubber used in a tire. Given the competitive tire market and the continued need to lower the cost of manufacturing tires without sacrificing properties, there exists a need to eliminate or substantially decrease the cost of innerliners which perform such an important function in the performance of a tire.